<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>Document</title>
        <style>
            .con{
                display: flex;
                flex-direction: row;
                justify-content: space-around;
                flex-wrap: wrap;
                height: 300px;
                width: 900px;
                margin: 0 auto;
                border: 1px solid forestgreen;
            }
            .con div{
                width: 100px;
                height: 100px;
                background-color: darkolivegreen;
                margin-top: 50px;
            }
        </style>
    </head>
    <body>
        <div id="con" class="con">
            <div></div>
            <div></div>
            <div></div>
            <div></div>
        </div>
    </body>
</html>